Separation Techniques

Key Concepts

Solid + Solid (magnetic)

• Use magnet

Solid + Solid (pressure changes)

• Pressure changes affect change in state.

• No liquid state in some substances at sea-level pressure (sublimation)

• Eg: mothballs (napthalene)

• Can use to separate mixtures

Solid CO2

Heavy solid + Liquid

• Decanting

• Pour liquid out, leaving solid behind in test-tube/beaker/conical flask etc

• Not good method to purify

Small solids + Liquid• Use filtration

• Filter paper, filter funnel, beaker/conical flask

• Note: Not everything can be filtered out. Depends on size of pores (“holes”) in filter paper

Solid (dissolve in water) + Liquid

• Eg: Sugar, salt

• Crystallisation

• Evaporate extra water in mixture. Let crystals form naturally.

Liquid + Liquid (can mix)

• Distillation AND fractional distillation

• Check boiling points of liquid first

• Different boiling point (more than 100C difference) => Distillation

• Miscible = Mix

Liquid + Liquid (Cannot mix)

• Eg: Water + Oil

• Immiscible = Cannot mix

• Separating funnel is used

Check how pure is substance

• Chromatography

• Separate parts of mixture using suitable liquid (solvent-dissolve solid or liquid) and solid (normally paper)

Solid + Solid

• Example: Salt + Sand

• How to get